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Unseptseptium
Unseptseptium, Uss, is the temporary name for element 177. NUCLEAR What follows is based on a first-order, liquid-drop assessment of where the outer boundary of the nuclear world is. Assume cautious values for how many neutrons a nucleus with 177 protons can bind (high neutron dripline) and how few it can have before it fissions immediately regardless of how much the structure it can develop stabilizes it (low must-fission curve). Assume, too, that anything that lasts long enough so that protons and neutrons can be treated as particles rather than collections of quarks (is causal) might be a nucleus. Under these conditions, Uss isotopes are theoretically possible between Uss 423 and Uss 771 (see "The Final Element", this wiki). Uss 423 through Uss 618 are expected to decay by beta emission if they don’t fission quickly. Above that value of A, the confident neutron dripline, drops may decay by neutron emission before they can fission. (Structural correction does not affect neutron emission.) Uss 618 itself requires 1.5 MeV of structural correction energy to survive for the 10^-14 sec needed to bind an electron and so qualify as a nucleus. Uss 685 and heavier don’t require any correction. Nuclear drops lighter than Uss 446 need more than twice the correction energy needed to prevent fission in worst-case nuclei in the A = 480 region(1). In between, it is not usually possible to determine whether structural corrections will stabilize nuclear drops against fission. Neutron shell closures have been predicted at N = 406(2),(3),(4), 370(4), 318(5), and 308(1). The isotope Uss 583 requires 1.5 MeV of structural correction, which means all isotopes in the Uss 573 to Uss 588 band are likely. Uss 547 requires 2.5 MeV of structural correction, which means all isotopes in the band Uss 537 to Uss 552 are also likely. All isotopes in both bands will probably beta-decay. Uss 495 requires 9.5 MeV of correction energy, and Uss 485 requires 12 MeV, which implies that some nuclides in the band Uss 475 to Uss 500 are possible if correction is strong. Alpha decay is to be expected in this band. Between Uss 446 and Uss 640 some drops may be nuclei. Outside this band, isotopes of Uss are nearly impossible. ATOMIC Electron structure of Uss has not been studied closely, but it is likely to differ significantly from the conventional orbitals found in lower-Z nuclei. While only the innermost electrons would be qualitatively different, other electrons are likely to be quantitatively different from those in lower-Z atoms. Uss is also large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Uss to have different electronic structures. (That means it is no longer an element in the chemical sense.) Predictions of atomic or chemical properties of Uss are risky. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Uss 573 to Uss 577 to form. It is probably impossible for lighter isotopes to form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Uss 573 to Uss 588, Uss 537 to Uss 552, and Uss 475 to Uss 500 bands. Quantities produced by this method are very small. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 3. “Search for Superheavy Elements Among Fossil Fission Tracks in Zircon”; J. Maly & D.R. Walz; Stanford Linear Accelerator Center publication SLAC-PUB-2554; July 1980. 4. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 5. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-09-19)